Recently, the development of alternative energy to oil is a very important issue, because of the concern related to transportation energy supply, such as large increases in oil prices and the petroleum depletion prediction in the near future (peak oil), as well as environmental problems such as global warming and aerial pollution. Plant biomass, or lignocellulose, is the most plentiful renewable energy source on earth, which is expected to serve as an alternative source to oil. The main components in the dry weight of biomass are polysaccharides such as celluloses and hemicelluloses, and lignin. For example, polysaccharides are used as a biofuel or a raw material of chemical products, after being hydrolyzed into monosaccharides such as glucose or xylose by glycoside hydrolases which are collectively referred to as cellulase enzymes.
Consequently, in the field of biorefining, it is important to develop a diverse range of highly active cellulase enzymes in order to efficiently carry out enzymatic hydrolysis treatment on cellulose-based biomass.
Lignocellulose is recalcitrant due to its highly complicated structures, and is hard to degrade with a single cellulolytic enzyme. Lignocellulose degradation to sugar requires at least three types of enzymes: endoglucanases (cellulase or endo-1,4-β-D-glucanase, EC 3.2.1.4) which randomly cut internal sites on cellulose chain, cellobiohydrolases (1,4-β-cellobiosidase or cellobiohydrolase, EC 3.2.1.91) which act as an exo-cellulase on the reducing or non-reducing ends of cellulose chain and release cellobiose as major products, and β-glucosidases (EC 3.2.1.21) which hydrolyze cellobiose to glucose. Besides, it is thought to be necessary to have an appropriate blending of a plurality of enzymes including xylanase (endo-1,4-β-xylanase, EC 3.2.1.8) which is a hemicellulase and other plant cell wall degrading enzymes.
On the other hand, Acremonium cellulolyticus is a filamentous fungus that produces a potent hydrolytic cellulase, and two types of cellobiohydrolase genes, 3 types of β-glucosidase genes and 7 types of endoglucanase genes have currently been isolated therefrom (see, for example, Patent Document 1). Endoglucanase is one of the glycoside hydrolases associated with the process of producing monosaccharides by randomly cleaving and degrading celluloses or lignocelluloses such as hemicellulose.